Polymer electrolyte membranes (PEMs) are used in fuel cells to provide proton conductivity between the fuel cell electrodes. In a typical polymer-electrolyte fuel cell (PEFC), the membrane structurally separates the electrodes of the fuel cell while providing a pathway for proton transport from one electrode to the other. For example in a hydrogen/oxygen fuel cell, hydrogen is catalytically oxidized at the anode side of the membrane-electrode assembly (MEA) forming H+ ions according to reaction (1).H2→2H++2e−  (1)
The formed protons permeate through the polymer electrolyte membrane to the cathode side, while electrons move along an external load circuit creating the current output of the fuel cell. At the cathode side of the MEA, reduction of oxygen occurs according to reaction (2).4H++4e−+O2→2H2O  (2)
Fuel cells transform the chemical energy liberated during the reaction of hydrogen and oxygen to electrical energy. Potentially, fuel cells can be used to provide power for buildings, transportation vehicles, electronic devices, etc.
The first polymer electrolyte fuel cells (PEFCs) were developed in the early 1960s and have been used in the NASA Gemini series of spacecraft. However, further commercialization of PEFCs beyond aerospace industry has been limited, in part, due to relatively low efficiencies of available PEFCs.